As is known, many food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or of mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH), which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
Once formed, the above packages may undergo further processing, such as applying a reclosable opening device to protect the food product inside the package from contact with external agents, and to enable the product to be poured out.
At present, the most commonly marketed opening devices comprise an annular frame defining a pour opening and fitted about a removable or pierceable portion of a top wall of the package; and a cap hinged or screwed to the frame, and which is removable to open the package.
The removable portion of the package may be defined by a sealing sheet glued or heat-sealed to the outside of the package to close a through hole in the package. One example of this solution is described and illustrated in Patent Application EP-A-9433549. Alternatively, the removable portion of the package may be defined by a so-called “prelaminated” hole, i.e. a hole formed in the base layer of the packaging material before covering the base layer with other layers defining the packaging material, e.g. the layers of thermoplastic material and/or the layer of barrier material, which close the hole hermetically.
In both cases, before being applied to the respective packages, the opening devices are fed successively through a gluing unit, in which they are coated with adhesive, usually hot-melt glue.
As described for example in Patent Application EP-A-1798149, on which the preamble of claim 1 is based, gluing units are known substantially comprising a conveyor for feeding the opening devices along a given path, and an adhesive dispenser, which interacts with each opening device to apply adhesive to a flat fastening portion of the opening device frame.
More specifically, the adhesive is applied by moving the dispenser along a flat application path parallel to the fastening portion plane.
Though reliable and efficient, the gluing units described still leave room for further improvement.
More specifically, a need is felt to apply the adhesive to the fastening portion along predetermined trajectories and in predetermined amounts as repeatably and controllably as possible.
This is particularly so in the case of opening devices comprising a frame straddling an edge between a first and second wall, e.g. the top wall and a top end portion of a lateral wall, of the package, and comprising a first and second portion at an angle to each other and glued to the first and second wall respectively by respective fastening portions inclined with respect to each other.